MB 320: Temporarily disable WebRTC and WDBA on Windows.

WebRTC should be re-enabled when tor-browser#42758 is resolved, and and
the default browser agent when in general we make this feature work
again.

mozconfig-windows-x86_64

@@ -22,3 +22,5 @@ ac_add_options --disable-notification-server
 # Let's make sure no preference is enabling either Adobe's or Google's CDM.
 ac_add_options --disable-eme
 
+# tor-browser#320: Temporarily disable until we resolve the mingw problems.
+ac_add_options --disable-default-browser-agent